When cementing a tubular, centralizers have been used to allow the cement to work its way fully around the tubular. Without centralizers, particularly if there is a deviation in the wellbore, there was a risk that the tubular would lay up against the borehole wall on the low side undermining the benefit of the cement in trying to seal around the tubular.
Centralizers of various types have been used in the past. The most common centralizers comprise a plurality of spaced flexible strips that extend longitudinally between a pair of end rings. The centralizers are slipped over the end of the tubular on makeup or get clamped to the tubular due to a hinge connection in each of the two end rings. These centralizers are typically made of steel. The problem with these centralizers arises if there is to be any pipe expansion. Expanding tubulars has become a more widely used procedure and such centralizers have been known to cause high stress areas on the underlying tubular during expansion to the point where the tubular can split or crack. Attempts to improve on the metal centralizers described above by making them from a polymeric material have had mixed results. The problem there has been that they are not strong enough to hold their shape to the extent that their main purpose of centralizing is defeated. Also, their geometric dimensions do not lend themselves to be run through the previous casing string and yet still have enough standoff for suitable centralization.
Centralizing devices have also been used that are bulky and that have many moving parts. These designs are expensive, require inordinate maintenance, and are simply too large to be of use in many applications. Some examples are U.S. Pat. No. 2,874,783 and PCT Application WO 94/13928.
Another centralizing technique for cementing tubulars has been to use telescoping cylinders that can be pushed out when the tubular is in position. These cylinders had removable barriers to let flow go through them after extension. One of their uses was to centralize a tubular prior to cementing. Some illustrations of this type of centralizing system can be found in U.S. Pat. Nos. 5,228,518; 5,346,016; 5,379,838; 5,224,556; and 5,165,478. None of these centralizers were used in combination with tubulars that were to be expanded. Yet, despite the use of extendable cylinders to centralize prior to cementing, in applications where the tubular was to be expanded after cementing there was either no attempt to cement in an inclined wellbore or centralizers that wrapped around the tubular and caused stress failures when expanded were used. As a result, poor cement distribution occurred that was compounded by the subsequent expansion of the tubular. What is needed and addressed by the present invention is an effective way to centralize a tubular before it is cemented and subsequently expanded even if it is disposed in a deviated bore. The method of the present invention is to centralize using telescoping cylinders and then with the cylinders extended to expand the tubular internally to compact the setting cement and provide a reliable seal of the tubular despite the angle of inclination of the associated wellbore. These and other aspects of the present invention will be more apparent to those skilled in the art from a review of the description of the preferred embodiment and the claims, which appear below.